1. Field of the Invention
The present invention relates to a method and an apparatus for load balancing in a cellular communication system. More particularly, the present invention relates to a method and an apparatus for controlling a load between two cells by changing a terminal's access from a cell having a large load to a cell having a small load through a network-initiated HandOver (HO) (or Base Station (BS)-initiated handover) in an Orthogonal Frequency Division Multiplexing (OFDM) based wireless communication system such as Worldwide Interoperability for Microwave Access (WiMAX)/Long Term Evolution (LTE).
2. Description of the Related Art
In a 4th Generation (4G) mobile communication system, such as Worldwide Interoperability for Microwave Access (WiMAX)/Long Term Evolution (LTE), services having various service qualities (referred to as Quality of Service (QoS)) having about a 100 Mbps transmission rate are provided to users.
Such a 4th generation mobile communication system uses an Orthogonal Frequency Division Multiplexing (OFDM) scheme which is useful for high speed data transmission in a wired or wireless channel.
The OFDM scheme, which is a scheme for transmitting data by using a multi-carrier, is a type of a Multi Carrier Modulation (MCM) scheme for converting symbol columns input in serial to symbol columns in parallel, for modulating the symbol columns into a plurality of subcarriers having orthogonality, that is, a plurality of subcarrier channels, and for transmitting the modulated subcarrier channels.
When loads are concentrated in a particular subcell (or carrier) due to load unbalancing in the cellular communication system, side effects such as a network entry failure, a call blockage, a call drop, QoS deterioration, a total throughput deterioration and the like may be generated. Accordingly, even though the need for load balancing exists, load balancing is not likely to be implemented due to a difference between costs (e.g., radio resources, backhaul link bandwidth resources, power spent on an operation of hardware and the like) spent on implementing the load balancing and the user distribution/bandwidth demand.
In order to perform the load balancing in such a cellular communication system, it is important to accurately express a load metric, which is a function indicating a load of each cell. Efficient load balancing is possible only if an accurately expressed load metric is used.
A load indicator for expressing the load has been investigated in the related art. However, a method of accurately expressing the load indicator has not been considered in the related art. Further, it has been assumed in the related art that the selection of a handover target base station is performed by a terminal, but it is difficult to apply the load balancing by the terminal in the 4th generation module communication system, such as WiMAX/LTE, having a centralized scheduling in which the base station has full authority for DownLink (DL)/UpLink (UL) resource allocation.
In addition, there are attempts to use a number of awake users accessing a cell in order to calculate the load metric, or use a DL/UL burst occupancy of the cell as an overall radio resource utilization. However, in the related art, a method of obtaining information on the number of awake users is not specifically described, and it is difficult to determine system loads in a packet based wireless communication system based only on the number of users that are merely awake. Further, it is difficult to determine actual load amounts for the efficient use of resources only by using the burst occupancy for the calculation of the load amounts in a system providing elastic traffic such as Internet traffic.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present invention.